Chapter 2: January 1, 2023

The history of timekeeping devices dates back to ancient civilizations observing astronomical bodies. Sundials and water clocks originated in ancient Egypt, while incense clocks were used in China. Mechanical clocks were developed in medieval Europe after the invention of the bell-striking alarm; Henry de Vick built a mechanical clock around 1360 that was the basis for improvements in timekeeping for the next 300 years. The mainspring, invented in the 15th century, allowed small clocks to be built. Leonardo da Vinci produced the earliest drawings of a pendulum. The pendulum clock, designed by Christiaan Huygens in 1656, was more accurate than other mechanical timekeepers. The electric clock, invented in 1840, controlled the most accurate pendulum clocks until the 1940s, when quartz timers became the basis for precise measurement of time and frequency. Atomic clocks are the most accurate timekeeping devices in practical use today and are used to calibrate timekeeping instruments.